Giải thích các bước giải:
$(\cos\dfrac{x}{4}-3\sin x)\sin x+(1+\sin\dfrac{x}{4}-\cos x)\cos x=0$
$\to \sin x\cos\dfrac{x}{4}-3\sin^2x+\cos x+\cos x\sin\dfrac{x}{4}-\cos^2x=0$
$\to (\sin x\cos\dfrac{x}{4}+\cos x\sin\dfrac{x}{4})+\cos x-\cos^2x-3\sin^2x=0$
$\to \sin(x+\dfrac{x}{4})+\cos x-(\cos^2x+\sin^2x)-2\sin^2x=0$
$\to \sin \dfrac{5x}{4}+\cos x-1-2\sin^2x=0$
$\to \sin \dfrac{5x}{4}+\cos x-1-2(1-\cos^2x)=0$
$\to \sin \dfrac{5x}{4}+\cos x+2\cos^2x-3=0$
